As a load measuring transducer generally employed in general-purpose electronic scales, industrial electronic scales and the like in the related art, there has been widely used a so-called “electric resistance type load cell” that employs a resistive wire constructing a strain gauge. In this load cell, when a strain is generated in a structure due to application of load to the structure, the strain is detected as a change in electric resistance of the resistive wire of the strain gauge and then converted into an electrical signal that in turn is measured, thereby measuring the applied load.
Load cells with accuracy as high as about between 1/3,000 and 1/5,000 are generally available. It is very difficult to implement a load cell with accuracy higher than the above accuracy. This is because there are problems in that a layer of an adhesive used to attach a strain gauge to a structure distorts and transfers a strain produced in the structure and also disturbs extension and compression behaviors of the structure. Further, since the adhesive is made of polymer and has an inhomogeneous amorphous structure, it has non-uniform mechanical properties that cannot be easily predicted.
Inherent features of a strain gauge itself also adversely affect the implementation of higher accuracy. This is because there is a problem in that a back plate which is made of polymer such as phenol or polyamide and placed below a resistive material of the strain gauge inhibits the transfer of a strain without distortion in the same manner as the layer of the adhesive.
Further, since it is difficult to achieve a uniform profile of the resistive material throughout the strain gauge, it is also difficult to obtain uniform deformation thereof proportional to a compressive or tensile strain of a structure.
Another prior technique for measuring load uses an electromagnetic force balancing type load measuring transducer. However, since this load measuring transducer employs a very complicated mechanical mechanism, the load measuring transducer is difficult to manufacture and is very expensive. In addition, there are electrical and spatial limitations on increase of electromagnetic force serving as balancing force for applied load. Further, since the complicated mechanical mechanism includes a lot of thin hinges, there are problems in that it is not suitable for measurement of heavy load and it is very vulnerable to external impact.
Due to the above difficulties or problems, such a load measuring transducer cannot be easily used in general-purpose commercial electronic scales or industrial electronic scales and also be restrictively used only in special-purpose electronic scales.
Furthermore, the load measuring transducer should be able to measure the applied load even when the load is applied eccentrically to a deformation-producing portion of the structure rather than at the center thereof.